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LEATHER  REFUSE; 


Its  Value  in  Agriculture. 


BY 


J.  B.  LINDSEYy  Ph.  D., 

MASSACHUSETTS  STATE  EXPERIMENT  STATION, 
AMHERST. 


W.   F.  HCMPHRSY, 
GENBVA,  N.  V. 
1894. 


L  L  f 


Agricultural  Science. 

Vol.  VIII.  FEBRUARY,  1894.  No.  2. 


LEATHER  REFUSE  — ITS  VALUE  IN  AGRICUL- 
TURE. 

BY  J.  B.  LINDSEY. 
First  Paper. 

During  the  past  few  years,  claims  have  been  made  at  various 
times  that  large  quantities  of  leather  shavings  and  the  like  have 
found  their  way  into  the  so-called  commercial  fertilizers  that  are 
so  widely  used  by  the  farmers  of  the  United  States.  The  writer 
has  no  means  of  knowing  whether  this  claim  is  true  or  not.  It 
should  be  the  object  of  the  fertilizer  manufacturer  to  utilize  all 
kinds  of  waste  products  that  possess  distinct  manurial  value. 
By  so  doing  he  not  only  benefits  himself,  but  the  farmer  as  well. 

It  was  very  early  assumed  from  its  chemical  character,  without 
any  exact  experiments  upon  which  to  base  the  assumption,  that 
leather  refuse  would  yield  its  nitrogen  as  plant  food  very  slowly 
if  at  all. 

Methods   Employed  to   Make   the    Nitrogen  Available  to 
Growing  Plants. 

The  first  method  suggested,  so  far  as  the  writer  has  been  able 
to  ascertain,  was  that  prescribed  by  F.  O.  Ward*,  of  England,  in 
1857,  for  turning  to  account  woolen  rags,  wool,  silk  and  leather 
clippings.  The  process  as  described  was  as  follows  :  The  refuse 
was  introduced  into  an  ordinary  autoclave  digester,  and  there 
kept  for  about  three  hours,  surrounded  by  steam  heated  to  a  pres- 
sure of  from  three  to  five  atmospheres.  Wool  required  a  higher 
temperature  than  leather,  and  silk  than  wool.  The  materials 
condensed  a  portion  of  the  steam, and  absorbed  its  heat.  This  joint 
action  converted  the  animal  matter  into  a  friable  substance, which, 

*  Report  by  the  Jtiries  of  the  International  Exhibition,  1862.  Reporter,  A. 
W.  Hoffman.    Repertory  of  Patent  Inventions,  Aug.  1857,  page  137. 


50  AGRICUI.TURAI,  SCIENCE.  Vol.  VIII.  No.  2. 

however,  still  retained  its  original  form  and  aspect.  It  was  then 
ground  fine,  sifted,  and  bagged.  "  The  details  of  the  process, the 
fuel-  and  labor-saving  arrangements  that  have  been  learned, point 
by  point,  by  costly  manufacturing  experience  cannot, ' '  says  Ward, 
' '  with  propriety  be  divulged, ' '  The  final  product  is  described  as  a 
dark  colored  powder.  The  nitrogen  in  the  finished  product  is 
said  to  exist  to  a  small  extent,  as  ready  formed  ammonia,  being 
in  combination  with  ulmic  and  humic  acids  developed  during  the 
process.  It  was  stated  at  the  time,  that  this  manufacturing 
process  was  carried  on  at  large  works  on  the  Thames.  The  ma- 
terial for  the  most  part  was  sold  to  manure  manufacturers,  who 
used  it  as  an  ingredient  of  their  several  fertilizing  compounds, 
and  it  was  ' '  used  by  many  farmers  who  are  not  aware  of  the  fact. ' ' 
Ward  says  that  ' '  while  this  material  is  not  as  active  as  some 
other  forms  of  organic  nitrogen,  it  possessed  distinct  value  as  a 
fertilizer."* 

Kdw.  Toynbect  in  1858,  also  described  a  process  whereby 
leather  and  wool  waste  could  be  cooked  in  sulfuric  acid,  and  be 
made  more  available  as  a  fertilizer.  He  said  "  that  to  one  cent- 
ner of  sulfuric  acid,  four  or  five  centners  of  wool  or  leather  waste 
could  be  added."  The  writer  does  not  see  how  such  a  large 
amount  of  leather  could  be  added  to  the  acid,  as  will  be  shown 
further  on.  L,.  MeyerJ  speaks  of  dissolving  all  such  refuse  sub- 
stances in  warm  sulfuric  acid,  and  neutralizing  the  moist  mass 
with  bone. 

A  Lipowitz§  notes  the  fact  that  the  Posner  fertilizer  factory 
utilizes  all  such  kinds  of  waste,  as  have  already  been  referred  to. 

Runge^  speaks  of  rendering  leather  and  wool  more  available, 
by  dissolving  them  in  a  mixture  of  Glauber's  salt  and  quicklime. 
This  chemist  manufactured  a  fertilizer  upon  a  large  scale  from 
these  materials. 

Reichardt*Mescribes  his  method  of  subjecting  the  leather  refuse 

*  The  writer  does  not  know  whether  this  process  is  still  in  operation  in 
England,  for  utilizing  the  leather,  wool,  and  silk  wastes. 

t  Repertory  of  Patent  Inventions  1858,  p.  389 ;  Jahresbericht  Agric. 
Chem.,  1859. 

t Jahresbericht  Agric.  Chem.,  1859,  228. 

I  Allgem.   Zeitung  fiir  deutsche  Land,  und  Forstwirthe,  1859,  153. 

^Jahresbericht  Agric.  Chem.,  1865. 

**  Zeitschrift  fiir  deutsche  Landwirtschaft,  1865,  136.  Jahresbericht  Agric 
Chem.,  1865. 


l894-  AGRICUI^TURAL  SCIENCE.  5 1 

to  steam  pressure,  and  then  drying  it  quickly.  After  such  a 
treatment  he  found  15.75  per  cent,  of  the  material  to  be  soluble  in 
boiling  water,  and  that  after  standing  for  some  time,  20  per  cent, 
could  be  dissolved.  By  treating  the  dry  leather  that  had  been  sub- 
jected to  steam,  with  20  to  40  per  cent,  sulfuric  acid,  he  was  ena- 
bled to  dissolve  from  22  to  29  per  cent,  of  the  leather  in  water. 
With  a  5  per  cent,  solution  of  crystallized  soda,  28.8  per  cent, 
could  be  brought  into  solution.  He  therefore  concluded  that 
the  best  method  was  to  subject  the  leather  to  the  action  of  a 
weak  soda  solution. 

Coignet's*  method  was  reported  in  1874  by  H.  Mangon. 
Briefly  stated,  it  is  as  follows  :  The  refuse  material  is  placed  in 
a  room  having  a  cubic  area  of  20  meters.  Directly  outside  of  the 
room  is  a  coke  oven,  connected  with  a  chimney  that  has  an  open- 
ing into  the  room  containing  the  material  to  be  treated.  Into 
this  chimney  are  conducted  jets  of  steam,  so  that  the  room  is 
heated  from  150°  to  160°  C.  for  several  hours  by  this  moist  chim- 
ney air.  Under  these  conditions  the  leather  swells  somewhat, 
and  becomes  dark,  brittle,  and  can  easily  be  rubbed  to  a  powder. 

Storerf  says,  "It  is  evidently  with  reference  to  this  process, 
that  the  statement  has  recently  been  made,  that  certain  manufac- 
turers of  fertilizers  at  Paris  devote  themselves  particularly  to  the 
preparation  of  torrefied  wool,  horn,  leather,  and  even  bone,  the 
leather  having  first  been  steamed  strongly  to  remove  oil  and  gela- 
tine." 

I^'Hotet  describes  a  method  whereby  such  waste  material  as 
wool,  leather,  etc.,  can  be  converted  into  sulfate  of  ammonia. 
He  suggests  dissolving  the  material  in  a  ten  per  cent,  solution  of 
caustic  soda  in  the  cold.  The  substances  will  be  partly  dissolved, 
or  their  structure  more  or  less  destroyed.  The  jelly-like  mass  is 
then  mixed  with  caustic  lime  till  it  becomes  of  a  doughy  consis- 
tency. It  is  then  brought  into  iron  retorts,  and  heated  at  first  at 
as  low  a  temperature  as  possible  in  order  to  prevent  the  dissocia- 
tion of  the  ammonia,  which  is  caught  in  sulfuric  acid.  After  the 
gas  has  been  nearly  driven  off,  the  retorts  are  subjected  to  red 

*  Organ  der  Verein  f.  Riibenz.  Industrie  in  CEster-Ungarn,  1874,  32. 
Jahresbericht  Agric.  Chem.  1873-1874,  37. 

^  Agriculture  1.,  382. 

X  Centralblatt  fiir  Agric.  Chem.  5,  258.  lUustrirte  landw.  Zeitung,  1874, 
No.  2.  18. 


52  AgricuIvTurai,  Science.        Vol.  viii.  No.  2. 

heat.  At  the  end  of  the  operation,  a  white  powdery  substance  is 
left  behind,  consisting  of  carbonate  of  soda  and  caustic  lime. 
By  cooking  this  substance  with  water,  caustic  soda  is  formed  and 
can  be  again  utilized.  By  this  method  all  the  nitrogen  is  obtained. 
The  resulting  sulfate  of  ammonia  is  somewhat  colored. 

For  utilizing  leather  Riimpler*  suggests  the  following  method  : 
In  lead  or  iron  jacketed  kettles,  sulfuric  acid  of  50°  B.  is  heated 
very  hot,  and  leather  stirred  in  till  a  dark  brown  fluid  is  obtained. 
This  fluid  is  then  used  to  dissolve  the  phosphate  of  lime.  He  re- 
marks that  ' '  the  nitrogen  is  saved,  and  without  doubt  is  much 
more  available  from  the  fact  that  the  tannin  is  destroyed." 

Brhardt  t  suggests  that  such  refuse  material  be  slowly  burned 
in  closed  ovens,  and  the  gas  collected  in  moist  muck,  till  the  lat- 
ter becomes  saturated.  This  muck  mixed  with  superphosphate 
gave,  he  says,  a  quick  acting  manure. 

DeherainJ  says  that  this  leather  refuse  can  be  dissolved  in  sul- 
furic acid,  and  the  excess  of  acid  neutralized  with  phosphate  of 
lime.  In  this  way  he  claims  a  very  active  fertilizer  can  be  ob- 
tained at  a  low  cost. 

The  writer  understands  that  this  latter  method  has  been  in  quite 
general  use  for  many  years  by  European  manufacturers.  Not 
only  has  leather  been  thus  treated,  but  also  a  great  variety  of 
nitrogen-containing  refuse  materials.  American  manufacturers 
also  subject  various  waste  materials  to  the  action  of  sulfuric  acid, 
in  order  to  render  them  more  quickly  available. 

From  the  many  methods  suggested  for  the  utilization  of  leather 
waste,  it  is  evident  that,  in  the  older  countries,  especially  Eng- 
land, France  and  Germany,  this  material  after  having  been  sub- 
mitted to  some  mode  of  treatment,  is  quite  generally  used,  to  a 
greater  or  less  degree,  in  the  manufacture  of  commercial  fertilizers. 

Petermann  §  says,  ' '  that  it  is  well-known  that  certain  Belgian 
and  French  manufacturers  use  leather  in  their  products,  but  that 
such  goods  contain,  in  addition,  nitrogen  in  other  forms,  such  as 
blood,  horn  meal,  sulfate  of  ammonia  and  nitrate  of  soda." 
He  further  states  that  the  "factories  producing  this  material  are 
numerous,  and  a  considerable  quantity  is  produced  annually." 

*Kaufliche  Diingestoffe.     H.  Riimpler,  1875  (Thaer   Bibliothek). 

t  Jahresbericht  Agric.  Chem.,  1880,  337. 

tDeherain,  Chimie  Agricole,  [1892],  624. 

I  Recherches  de  Chimie  et  Physiologic  [1886],  144. 


i894-  Agricultural  Scienck.  53 

Manurial  Value  of  Prepared  Leather  Waste. 

The  different  experiments  made  to  prove  the  value  of  leather 
have  been  conducted  either  with  untreated  finely  ground  leather, 
with  torrefied  leather,  or  with  leather  steamed  under  pressure. 

Three  different  methods  have  been  used,  in  testing  the  agri- 
cultural value  of  leather:  (a)  by  directly  testing  its  fertilizing  effect 
either  in  pot  or  plat  experiments  ;  (b)  by  artificially  digesting  it 
with  a  pepsin  solution  ;  (c)  by  noting  the  length  of  time  required 
to  nitrify  it.  The  first  method  is  by  far  the  most  interesting,  and 
leads  to  direct  results.  The  other  two  serve  at  least  to  confirm 
the  results  obtained  by  the  first  method. 

(a)     Pot  and  Plat  Experiments. 

Very  early  experiments  are  not  to  be  found  in  the  literature. 

The  first  experiment  recorded  was  made  by  Ladureau,*  and 
lasted  but  a  single  season.  He  found  that  2500  kilos,  of  torrefied 
leather  yielded  30,100  kilos,  of  sugar  beets,  testing  8.83  per  cent, 
of  sugar,  and  2500  kilos,  of  the  same  leather  plus  200  hectolitres 
of  lime  gave  38,600  kilos,  of  beets,  with  10. 10  per  cent,  sugar. 
The  same  area  of  land  without  leather,  yielded  20,000  kilos,  of 
sugar  beets  testing  10.93  percent,  sugar.  Petermann  remarks  on 
these  results  as  follows  :  "  In  spite  of  the  increased  yield  obtained 
by  using  the  leather,  the  experiment  was  not  a  success  financially 
and  further,  the  beets  produced  with  the  aid  of  the  leather  were 
poorer  in  quality  than  those  without  it." 

In  1880,  Petermann  t  carried  out  a  series  of  experiments  with 
ground,  steamed  leather,  to  test  its  manurial  value.  It  was 
very  dry  and  brittle,  and  contained  7.51  per  cent,  of  nitrogen  and 
0.81  per  cent,  of  phosphoric  anhydride  soluble  in  hydrochloric 
acid. 

The  experiments  were  carried  on  in  the  plant  house  in  pots, 
with  oats  ;  in  the  garden,  with  the  horse  bean  {Vidafaba)  ;  and 
in  the  field,  with  sugar  beets, 

/.     Experiments  with  Oats  in  Pots. 

Kach  test  was  made  in  duplicate.  The  soil  was  what  might  be 
called  a  sandy  clay,  each  pot  holding  4,000  grammes.  The  ferti- 
lizer was  mixed  with  three-fourths  of  the  soil  of  each  pot.  To  the  soil 

*  Annales  Agron.,  1878  ;  Loc.  cit.,  146. 

t  Loc.  cit.,  144,  Centralbl.  Agrie.  Chem.  10,  590. 


54  Agricultural  Science  Vol.  viii.  No.  2. 

ineacli  pot  were  added  0,25  gramme  of  nitrogen,  0.30  gramme  of 
phosphoric  acid,  and  0.20  gramme  of  potash. 

Resui,ts — Average  oe  the  Duplicates,  Expressed   in  Grammes. 

Entire  plant.        Straw.        ChaflF.        Grain. 
Unmanured 22.34        15.19        0.95  6.20 

Series  i. 
Nitrogen 

(a)  Leather 34.85        26.65        1.25  6.95 

(b)  Dried  blood 5i-9i        36.68        1.82        13.41 

Series  ii. 
Nitrogen  +  Phosphoric  Acid. 

(a)  Zi?a/A(?r  +  precipitated  phosphate.. 39. 93        31.28        1.15  7.50 

(b)  Blood  +  precipitated  phosphate 51.97        36.45         1.91         13.61 

Series  hi. 

Nitrogen  +  Phosphoric  Acid  +  Potash. 

(a)  Leather  +  precipitated  phosphate 

+  muriate  of  potash A30.55        21.90        1.09  7.56 

(b)  Dried Iblood  +  precipitated  phos- 
phate +  muriate  of  potash 37.40         29.65         1.82        15.93 

In  observing  the  results  of  the  experiments,  we  notice  especially 
with  reference  to  the  grain  produced,  that  the  leather  did  not 
increase  the  yield  to  any  appreciable  extent  over  that  of  the 
unfertilized  pots.  When  phosphoric  acid  and  potash  were  applied 
with  the  leather,  a  slight  increase  in  the  yield  of  grain  was  noticed, 
while  in  case  of  the  dried  blood  plus  the  phosphoric  acid  and  pot- 
ash, the  yield  was  twice  that  of  the  unfertilized  pot. 

(b)     Garden  Experiments  with  Horsebeans. 

The  soil  was  the  same  as  in  the  previous  experiment,     Size  of 

plats,  60  sq.   meters.      The    fertilizer    applied  was  leather  and 

nitrate  of  soda.     Nitrogen  was  applied  at  the  rate  of  58.5  lbs.  per 

acre. 

Results  per  Plat. 

stems  and  pods        Beans  in        Beans  per  acre 
in  kilos.  kilos.  in  kilos. 

Unmanured 9,869  1,131  37.7oo 

Leather 12,822  1,178  39.268 

Nitrate  of  soda 11,465  2,035  67,832 

It  will  be  observed  that  the  leather  produced  only  a  slight 
increase  in  the  yield  of  beans. 


1 894-  Agricultural  Science.  55 

(c)     Field  Experiments  with  Sugar-beets. 
Same  soil  as  in  previous  experiments.     Kach  plat  measured  i 
ar.     The  fertilizer  was  applied  at  the  rate  of  42^  pounds  of 
nitrogen,  and  528  pounds  of  phosphoric  acid  per  acre. 
Resui,ts  per  Hectare. 

Percentage 
Kilos.  increase  over 

unmanured. 

Unmanured 34)830  

Soluble  phos.  acid 34.38o  —1.5 

Water  and  citrate  sol.  phos.  acid 34,290  — 1.2 

Citrate  sol.  phos.  acid 34,38o  — 1.5 

Unmanured 33,840  

Leather  +  sol.  phos.  acid 37,890  '  11. 9 

Leather  -\-  water  sol.  +  citrate  sol.  phos.  acid 37, 180  10.7 

Leather-!-  citrate  sol.  phos.  acid 35,9^0  6.0 

Unmanured   32,940  

Nitrate  of  soda  -f-  sol.  phos.  acid 43,38o  28.1 

Nitrate  of  soda  +  water  -|-  citrate  sol.  phos.  acid 42,070  24.2 

Nitrate  of  soda  -f-  citrate  sol.  phos.  acid 43,830  29.4 

While  the  leather  has  shown  its  effect,  it  runs  far  behind  the 
nitrate  of  soda.  Petermann  says  that  from  a  financial  standpoint 
the  leather  shows  a  loss  and  the  nitrate  of  soda  a  gain.  Of  his 
results  the  experimenter  makes  the  following  resume  : 

"  With  horsebean,  the  leather  shows  practically  no  influence 
the  first  year.  With  oats  and  sugar  beets  an  increase  is  noted, 
but  this  is  slight  when  compared  with  that  from  blood  and  nitrate 
of  soda."  In  a  later  publication,  Petermann  says  that  in  his 
experiments  from  1 880-1 885,  the  various  forms  of  nitrogen  have 
shown  the  following  relative  worth  :  i .  Nitrate  of  soda  ;  2.  blood; 
3.  dissolved  wool ;    4.    ground  bone  ;    5.  raw  wool ;    6.  leather. 

Deherain*  gives  the  results  of  the  following  experiments  con- 
ducted in  the  field  at  Grignon  with  ground  leather.  The  results 
with  wheat  in  1880  and  1881,  show  the  residual  effect  of  that 
applied  to  potatoes  in  1879  : 

Potatoes.  Wheat. 


Hectolitres.    Grain,  Straw.  Grain.  Straw. 

Qtm.*  Otm.  Qtm.  Qtm. 

Unfertilized.-. 224            25.0  37.25  164  20.5 

Leather,  2000  kilos  295             27.5  40,00  23.4  38.7 

Leather,  1000  kilos 277             25,0  38.00  23  37.6 

*  Qtm.  =  quintal  metrique  =  100  kilograms. 

Deherain  remarks  that  his  experiments  make  it  clear  that  the 

*  Chimie  A^ricole  (  1892),  619. 


(Dry  Matter). 

1889. 

Average  of 

Kilos. 

both  years. 

47 

190 

48 

178 

52 

175 

61 

152 

43 

102 

56  Agriculturai<  Science.         voi.  viii.  No.  2. 

leather  yields  its  nitrogen  very  slowly.     He  does  not  state  whether 
the  leather  used  had  been  steamed,  roasted,  or  was  untreated. 

Miintz*  and  Girard,  in  connection  with  their  experiments  on 
the  nitrification  of  various  nitrogen-containing  organic  sub- 
stances, carried  out  also  a  series  of  field  experiments  with  various 
nitrogenous  materials.  Each  plat  had  an  area  of  one  ar.  and 
received  1.25  kilos  of  nitrogen  the  first  year,  together  with  the 
necessary  quantity  of  phosphoric  acid  and  potash.  No  manure 
was  applied  the  second  year.  The  soil  was  light  and  sandy, 
being  quite  favorable  to  nitrification.  The  plats  were  planted 
with  fodder  com  during  both  years. 

Fodder  Corn  Grown  Upon  One  Ar. 

1888. 

Form  of  nitrogen.  Kilos. 

Nitrate  of  soda 143 

Dried  blood 130 

Roasted  horn 123 

Roasted  leather 91 

No  nitrogen 59 

The  above  results  show  that  leather  even  when  roasted  is  quite 
inferior  in  its  action  to  dried  blood  and  nitrate  of  soda. 

Marckerf  gives  the  following  results  obtained  by  Seyffert,  at 
Halle,  with  cole-rape  : 

Form  of  nitrogen.  Yield  in  grammes. 

No  nitrogen 75.5 

riveather 469 

,,        ..  Steamed  bone  meal 1,572 

No  nitrogen  j  ^^^^^ ^;g^^ 

[^Nitrate  soda 2,607.5 

In  order  to  control  the  above  experiment  another  test  was  car- 
ried out  with  oats  by  Julius  Albert-Miinchenhof. 

YlEl<D. 

Form  of  nitrogen.  Grain.  Straw.  Roots.  Total. 

Grammes.  Grammes.  Grammes.  Grammes 

No  nitrogen 5.2  15.7  14.3  38.2 

Nitrate  of  soda 48.9  62.6  27.9  139-4 

Dried  blood 24.8  44.5  18.5  87.8 

Iveather 13.3  22.2  13.6  49.1 

"      fermented 21.5  36.4  17.2  75.1 

Marcker  remarks  that  leather  produced  but  a  slight  increase 
over  the  unfertilized,  and  that  the  quality  of  the  grain  was  poor- 
est when  not  any  nitrogen  was  used,  or  when  leather  was  applied. 

*Ann.  Agron.,  17,  289-304;  Biedermann's  Centralblatt,  20,  656. 
tjahresbericht  Agr.  Chemie,  1883,  241. 


Average 

Average 

and  2d  year. 

three  years. 

lOO 

100 

67 

69 

59 

64 

53 

61 

12 

20 

1894.  Agricultural  Science.  57 

Wagner*  has  made  an  exhaustive  study  of  the  value  of  diflfer- 
ent  forms  of  nitrogen,  having  conducted  366  plat  and  pot  experi- 
ments. The  experiments  were  carried  on  for  several  successive 
years  in  a  soil  rich  enough  in  lime  to  favor  nitrification,  and 
every  effort  was  made  to  have  the  conditions  equal  in  all  cases. 
But  a  very  brief  resume  can  be  given  at  this  time.  One  experi- 
ment was  conducted  for  three  successive  years  upon  small  plots 
of  soil.  Summer  rye  was  planted  the  first  year,  summer  wheat 
the  second,  and  carrots  the  third  year.  Placing  the  value  of  the 
returns  from  the  nitrate  of  soda  plats  at  100,  the  other  forms  of 
nitrogen  had  the  following  relative  worth  : 

I  St  year. 

Nitrate  of  soda 100 

Blood 67 

Fish 51 

Steatned  bone  meal 42 

Leather 13 

Experiments  were  also  conducted  in  pots  with  various  soils, 
but  the  results  cannot  be  noticed  here. 

In   concluding  his  remarks  relative  to  this  subject  Wagner 
says,  "When  I  take  all  things  into  consideration 
I  think  I  may  present  the  following  figures,  as  an  expression  of 
the  relative  value  of  nitrogen  in  different  forms  of  nitrogen-con- 
taining material  : 

Nitrate  of  soda  lOO 

Sulfate  of  ammonia 90 

Blood,  horn  meal  and  green  crops 70 

Fine  ground  bone,  fish  and  tankage 60 

Stable  manure 45 

Wool  dust 30 

Leather 20 

So  far  as  the  writer  has  been  able  to  ascertain,  Wagner  does 
not  state  the  form  of  the  leather  used. 

Taking  the  price  of  nitrogen  in  nitrate  of  soda  at  14.8  cents,  a 
pound  of  nitrogen  in  stable  manure  would  be  worth  6.7  cents, 
and  in  leather  2.8  cents. 

Note  by  the  Editor  :  From  this  resume  of  direct  tests  of  the  fertilizer 
value  of  leather,  the  experiments  of  F.  H.  Storer  {Bulletin  of  the  Bussey 
Institution,  2,  58-71)  should  not  fail  of  mention.  He  tested  the  manurial 
effect  of  sheep-skin  and  sole-leather,  raw  and  roasted,  on  several  soils  in 
pots,  applying  various  phosphatic  and  potassic  salts  in  solution.     The  crop 

*  Die  Stickstoffdungung  der  Landw.  Kulturpflanzen,  p.  242. 


58  Agriculturai.  Science.  voi.  viii.  No.  2. 

used  was  buckwheat.     The  results  were  as  follows  (expressed  in  weight  of 
total  crop  in  grammes)  : 

with  phos- 
phate of 
With  With  With  potash  and 

rain-  sulfate  phosphate  nitrate  of 

water.         of  potash.        of  potash.  lime. 

No  leather  used : 

In  Berkshire  sand. 0.200  0.200  0.155  0.665* 

In  Provincetown  sand 0,170  0.165  3.050 

In  loam  and  sand 0.270  0.160  5-830 

Raw  sheep-skin  (20)  : 

In  Berkshire  sand  (1300)....    o.ioo  0.130  0.055  0.640* 

In  Provincetown  sand  (1450)    0.080  o.  ico  1.400 

In  loam  and  sand  (1320) 0.170  0.120  4.020 

Raw  sole  leather  (40) : 

In  Berkshire  sand  (1300)....    o.iio  0.115  0.120  0.280 

In  Provincetown  sand  (1450)    0.120  o.iio  2.820 

In  loam  and  sand  (1320) 0.130  0.150  3.720 

Roasted  sheep-skin  (20) : 

In  Berkshire  sand  (1300)  ...    0.105  0.190  0.060  0.250 

In  Provincetown  sand  (1450)    0.250*  0470*  0.345* 

In  loam  and  sand  (1320) 0.850  0.700  3.060 

Roasted  sole-leather  (40)  : 

In  Berkshire  sand  (1300)....    0.220*         0.23Q  0.210*  0.360* 

In  Provincetown  sand  (1450)    0.910  i-750  3.120 

In  loam  and  sand  (1320) 2.120  1.980  4.785 

*  Immature  when  harvested. 

Storer  says:  "It  will  be  seen  plainly  enough,  that  while  neither  the 
sheep-skin  nor  the  sole-leather  supplied  any  nitrogenous  food  to  the  buck- 
wheat plants,  some  nitrogen  was  unquestionably  obtained  by  the  plants 
from  the  roasted  leathers  ;  a  little  from  the  roasted  sheep-skin  and  a  deci- 
dedly larger  amount  from  the  roasted  sole-leather.  ...  In  all  cases, 
the  light  bulky  material  tended  to  interfere  with  the  growth  of  the  plants. 
The  roast-leather  jars  exhibited  a  marked  growth  of  fungus,  the  raw  leather 
jars  showed  none,  corroborating  the  evidence  as  to  the  existence  of  available 
products  in  the  roast  leather.  There  is  but  little  in  the  results  above  given 
to  encourage  the  belief  that  roasted  leather  can  have  any  definite  money 
value  as  a  manure." 

(b)  Artificial  Digestion  Experiments  with  Leather. 
Stutzer  and  Klinkenberg^  were  the  first  to  propose  this  method. 
They  argued  that  the  amount  of  nitrogenous  material  that 
could  be  dissolved  or  digested  would  give  a  fairly  correct  idea  of 
the  value  of  the  substance  as  a  source  of  nitrogen  for  growing 
plants.  They  prepared  the  digestive  fluid  by  extracting  the 
inner  lining  of  a  pig's  stomach,  cut  fiue,  with  5  litres  of  0.2  per  • 
cent,  hydrochloric  acid  for  two  days,  filtering  the  solution,  and 
preserving  in  glass  stoppered  bottles,  adding  a  few  grammes  of  sal- 

*Joiurnal  fiir  Landw.,  1882,  p.  365.     Konig's  Vntersuchung  Landw.  und 
Gewerblich.  Wichtiger  Sioffe,  p.  219. 


i894-  AgriCULTURAI.  SCIENCE.  59 

icylic  acid  to  prevent  fermentation.  They  submitted  a  variety  of 
materials  to  the  action  of  this  solution.  A  few  results  are  given 
below: 

Per  cent,  of  nitro- 
Substance.  gen  digested. 

Blood 89.75 

Leather  (cooked,  and  then  roasted) 39-19 

Raw  bone 98.70 

Steamed  bone 90.50 

Drs.  Shepard  and  Chazal*  afterwards  submitted  a  great  variety 
of  nitrogen-containing  materials  to  the  action  of  Stutzer's  solu- 
tion.    Several  of  the  results  obtained  are  presented  below. 

Per  cent,  of  nitro- 
gen digested. 

Roasted  leather  meal* 37-8o 

Dried  blood  (black) 78.61 

Fish  scrap 88.67 

*  The  author's  remark  that  "this  prepared  leather  was  an  excellent  article,  so  far  as 
preparation  goes,  and  one  capable  of  being  used  in  the  fertilizer  trade,  without  much  fear  of 
detection." 

Johnson,  Farrington  and  Wintonf,  instead  of  using  Stutzer's 
solution,  dissolved  5  grammes  of  Golden  Scale  Pepsin  in  1000  c.c. 
of  0.2  per  cent,  hydrochloric  acid  and  digested  a  variety  of  sub- 
stances in  this  fluid.  Their  investigation  is  the  most  valuable  we 
possess  in  this  direction.     A  few  of  their  results  may  be  cited. 

Per  cent,  of  nitro- 
gen digested. 

Dried  blood  (two  samples) - 97.30 

Dry  ground  fish 71.20 

Leather  No.  ?,* , 23.40 

Leather  treated  by  benzine  process 35-90 

Leather  treated  by  superheated  steam 33-30 

Mixed  fertilizer  A  containing  2.02  per  cent,  leather 

nitrogen 23.40 

Mixed  fertilizer  B  containing  200  per  cent,  leather  ni- 
trogen and  1.75  per  cent,  blood  nitrogen 55- 60 

*  Fine  and  brittle,  but  method  of  preparation  not  known. 

In  this  connection  it  might  be  in  place  to  mention  the  experi- 
ments recorded  on  the  putrefaction  of  ammoniates,  at  first  suggested 
by  A.  Morgen.  J  He  put  leather  and  horn  meal  in  water  to  which 
a  small  amount  of  fecal  extract  had  been  added,  and  then  allowed 
the  solution  to  .stand  for  31  days  at  30°  C.  The  nitrogen  made 
solution  was  then  estimated. 

*See  Report  of  Conn.  Experiment  Sta.,  1885,  p.  117. 

■f  Loc.  cit. 

X  Landw.  Vers.  Stat.,  1880,  50  ;     Biedermann's  Centralblatt,  9,  801. 


6o  Agricultural  Science.        Voi.  viii.  No.  2. 

In  experiment  I=io  grammes  material  -|-  looo  cc.m.  water  were  used. 

In  experiment  11=5  grammes  material  +  looo  cc.m.  water  +  5  cc.m.  fecal 

extract. 
In  experiment  III,  the  same  with  10  grammes  material  +  5   cc.m.  fecal 

extract. 

Per  cent,  of 
soluble  nitrogen . 

Leather  meal,  average  of  3  experiments 34-56 

Horn  meal,  average  of  3  experiments 61.62 

Johnson*  repeated  Morgen's  work  on  a  very  large  number  of 

substances  ;  a  few  of  the  results  are  given  below.     He  allowed 

his  solution  to  stand  two  weeks. 

Per  cent,  nitrogen 
soluble. 

Blood 76.80 

Fish 78.10 

Fish 54.60 

Bone 79.00 

Leather,  No.  3 12.20 

Steamed  leather 42.30 

* '  Prepared  ammoniate ' '  (probably  leather) 35-70 

Johnson  remarks  that  "this  test  of  putrefaction  draws  the  same 

line  between  those  classes  of  ammoniates  that  was  drawn  by  the 

pepsin  digestion." 

(c)     Nitrification  Experiments  with  Leather. 

These  experiments  were  carried  out  by  Miintz  and  Girardf 
with  quite  a  number  of  nitrogen-containing  substances.  They 
were  conducted  in  the  laboratory,  and  care  was  taken  to  see  that 
the  soil  was  properly  aired,  and  that  moisture,  temperature,  etc. , 
were  favorable  to  the  experiment.  Ordinary  soil  was  at  first  used, 
the  amount  of  nitrates  present  being  carefully  noted  and  a  small 
amount  of  the  substances  to  be  nitrified  then  added.  After  a 
certain  time,  the  nitrates  were  washed  out  with  water  and  esti- 
mated. A  very  short  resume  is  here  presented  : 
Nitrogen   Nitrified,  per    100  Parts  of  Nitrogen  Added   to  the 

Soil. 

I.  II.  III. 

30  days.  39  days.  32  days. 

Sulfate  of  ammonia 75  83.76  83,76 

Dried  blood 72.44  73-56  84.50 

Roasted  horn 71.03  73-17  46.82 

Roasted  leather 11.62  16.47  13.26 

In  order  to  study  the  influence  of  different  kinds  of  soil  upon 

the  process  of  nitrification,  the  experiment  was  repeated  with  soils 

from  various  sections  of  the  country. 

*  Loc  cit. 

fAnn.  Agron.   17,   290;    Agric.   Science,  7,  408-12;    Deherain,  Chimie 
Agricole.  p.  621. 


i894.  Agricultural  Science.  6i 

Nitric  Nitrogen  Found  in  Different  Soiw  Within  a  Certain  Time, 

Marsh  soil, 

Light  soil  Chalky  Garden  Very  heavy  sour, 

of  Joinville.  soil.  earth.  limey  clay.  Bretagne. 

Grammes.  Gram.m.es.  Grammes.  Grammes.  Grammes. 

Sulfate  of  ammonia...  2.69  1.78  0.51  None 

Blood 1.62  .73  .036  " 

Roasted  horn 1.22  1.08                .029  " 

Roasted  leather 0.41  0.24  0.55                .036  " 

These  experiments  in  general  coincide  with  field  and  pot  ex- 
periments as  well  as  with  artificial  digestion  experiments.  It  is 
worthy  of  note,  that  the  light  sandy  soil  was  most  favorable  to 
the  process  of  nitrification,  while  the  very  heavy  clay,  and  espe- 
cially the  sour  marshy  soil  was  decidedly  unfavorable  to  the  action 
of  nitrifying  organisms. 


98  AgricuIvTurai,  Scie;nce.  Vol.  VIII.  No.  3. 


.^ 


LEATHER  REFUSE— ITS  VALUE  IN  AGRICUL- 
TURE. 

BY  J.    B.    LINDSEY. 

Second  Paper. 

Notes  on  Work  Done  with  Leather  at  the  Massachusetts 

State  Experiment  Station. 

It  is  desired  at  this  time  to  refer  briefly  to  some  tests  carried 

out  by  the  writer  at  the  above  station. 

Can  leather  be  identified  in  fertilizer  mixtures  f 

If  one  were  to  depend  upon  the  microscope,  it  would  certainly 

be  an  impossibility  to  recognize  leather  in  finely  ground  fertilizer 


i894-  AgrICULTURAI,  SCIENCE.  '  99 

mixtures.  Even  if  material  of  a  fibrous  structure  were  detected, 
it  would  be  nothing  strange,  for  all  flesh  presents  such  a  struc- 
ture. After  leather  has  been  submitted  to  heat  or  pressure,  all 
structure  is  destroyed.  Able  microscopists  who  have  attempted 
to  identify  the  leather  under  the  microscope,  report  it  an  impossi- 
bility. 

With  chemical  reagents,  one  is  more  successful.  At  least,  tan- 
nic or  gallic  acids,  from  their  well  known  reaction  with  an  iron 
salt,  are  easily  recognized,  and  while  one  perhaps  could  not  posi- 
tively declare  that  the  tannic  or  gallic  acids  present  were  derived 
from  leather,  it  certainly  would  be  highly  probable. 

Dr.  C.  W.  Dabney,*  when  director  of  the  North  Carolina  Ex- 
periment Station,  published  a  bulletin  in  which  he  suggests  that 
the  best  reagent  for  recognizing  the  tannic  acid,  is  a  phosporic 
acid  solution  of  phosphate  of  iron.  He  states  that  if  leather  be 
present  in  the  substance  examined,  a  purple  color  will  soon  ap- 
pear, if  a  few  drops  of  this  solution  be  added  to  the  alkaline  solu- 
tion of  the  leather  extract.  I  prepared  the  phosphoric  acid  solu- 
tion of  phosphate  of  iron  as  follows  :  Ten  grams  of  ferric  chloride 
were  dissolved  in  water  and  sodium  phosphate  added  till  all  the 
iron  was  precipitated  as  phosphate  of  iron.  The  phosphate  of 
iron  must  be  freshly  prepared,  otherwise  it  will  dissolve  slowly, 
if  at  all.  The  phosphate  of  iron  was  filtered  and  washed  quite 
thoroughly  with  water,  and  both  filter  and  precipitate  brought  into 
a  beaker  containing  400  c.c.  of  water  to  which  had  been  added 
40  grams  of  glacial  phosphoric  acid.  A  gentle  heat  dissolves  the 
iron  phosphate  quite  readily. 

If  a  drop  of  pyrogallic  acid  is  added  to  water,  the  solution 
made  slightly  alkaline  with  ammonia,  and  then  a  cubic  centimeter 
of  the  iron  phosphate  solution  added,  a  dark  purple  color  appears. 
If  tannic  acid  is  substituted  for  the  pyrogallic  acid,  a  dark  wine 
color  results.  In  order  to  recognize  leather  in  a  mixture,  a  small 
amount  (i  gramme)  of  the  substance  supposed  to  contain  it,  is 
placed  in  a  beaker  with  30-40  c.c.  of  water,  a  few  drops  of  sulfuric 
acid  added,  the  liquid  brought  to  boiling,  filtered,  a  little  of  the 
iron  phosphate  solution  added,  and  the  solution  then  made  slightly 
alkaline  with  ammonia.  If  leather  is  present,  a  dark  purple  to 
wine  color  will  soon  appear. 

*Nortli  Carolina  Bxpt.  Sta.  Bull.  No.  3,  1883  :  Horn,  Leather  and  Wool 
Waste. 


loo  Agricultural  Science.         Vol.  viii.  No.  3. 

Should  leather  be  present  in  a  mixed  fertilizer  containing  solu- 
ble phosphate  of  lime,  the  latter  will  of  course  be  precipitated  on 
the  addition  of  ammonia,  but  this  in  no  way  interferes  with  the 
color  reaction.  The  writer  examined  during  the  summer  of  1893 
quite  a  number  of  fertilizers  ofiScially  collected  in  Massachusetts, 
but  in  no  case  was  leather  to  be  detected.  When,  however,  10 
per  cent,  of  leather  was  added  to  a  mixed  fertilizer,  and  then 
tested  with  the  phosphate  of  iron  solution,  the  dark  color,  due  to 
the  presence  of  tannic  or  gallic  acids  very  distinctly  appeared. 

During  the  early  summer  of  1893  several  samples  of  leather 
were  received  at  the  station.  It  was  stated  that  large  quantities 
of  the  material  were  on  the  market,  and  one  could  surmise  at 
least  that  it  might  be  used  as  a  source  of  nitrogen  in  the  manu- 
facture of  commercial  fertilizers,  organic  nitrogen  at  the  time 
being  quite  high  in  price.  It  was  thought  wise  to  submit  the 
samples  to  several  tests,  and  for  the  sake  of  comparison,  pure 
sole  leather  obtained  by  the  writer  at  the  cobbler's,  and  dried 
blood  were  also  included. 

Description  of  the  Samples. 

I.  Sole  leather. 

This  leather  was  ground  fine  for  future  tests.  Under  the  micro- 
scope it  showed  a  distinct  fibrous  structure.  It  contained  2.76 
per  cent,  of  fat  and  7.94  per  cent,  of  nitrogen. 

II.  Steamed  leather. 

Some  of  the  finely  ground  leather  was  placed  in  pressure  bot- 
tles, water  added,  and  heated  for  6  hours  at  110°  C.  The  leather 
was  virtually  subjected  to  three  atmospheres  of  steam  pressure. 
After  treatment  it  had  become  very  dark  in  color  and  appeared  as  a 
jelly-like,  amorphous  mass.  The  microscope  showed  it  to  be  de- 
void of  any  fibrous  structure.  The  tannic  or  gallic  acids  were 
still  easily  recognized,  showing  that  they  had  not  been  destioyed 
by  the  heat  and  pressure.  When  dry,  it  became  quite  brittle, 
crumbling  easily. 

III.  Coarse  leather  sent  to  the  station. 

This  leather  came  in  pieces,  from  the  size  of  a  walnut  to  that 
of  a  small  hen's  egg.  It  contained  37,47  per  cent,  of  fat  and  4.52 
per  cent,  of  nitrogen.  The  large  amount  of  fat  completely  con- 
cealed its  structure. 


i894-  Agricultural  Science.  ioi 

IV.  Philadelphia  Tankage. 

The  sample  was  very  finely  ground  and  quite  dry.  It  con- 
tained 1.95  per  cent,  of  fat,  7.80  per  cent,  of  nitrogen  and  traces 
only  of  phosphoric  acid.  Its  smell  and  general  appearance  indi- 
cated clearly  that  it  was  leather  that  had  been  roasted  or  steamed. 
To  the  eye  it  appeared  to  be  lacking  in  fibrous  structure,  and 
with  the  microscope  it  appeared  simply  as  a  gelatinous  mass. 

V.  Dried  blood. 

It  was  an  excellent  sample,  containing  12.71  per  cent,  of  nitro- 
gen and  0.64  per  cent,  of  fat. 

Artificial  Digestion  of  Different  Leathers. 

The  artificial  digestion  of  the  substances  above  described  was 
carried  out  according  toStutzer's  method.  In  the  first  series  of 
trials  both  the  pepsin  and  pancreas  solutions  were  used.  The 
preparation  of  the  pepsin  solution  has  already  been  described. 

The  pancreas  solution  was  prepared  by  taking  the  fresh  pan- 
creas of  an  ox,  cutting  it  fine,  mixing  it  with  sand  and  allowing 
it  to  stand  24  to  36  hours  exposed  to  the  air.  It  was  then  rubbed 
with  lime  water  and  glycerine  (to  every  1,000  gm.  of  the  pan- 
creas-sand mixture  use  3  litres  of  lime  water  and  one  litre  of  gly- 
cerine of  1.23  sp.  gr.),  and  the  resulting  fluid  allowed  to  stand 
with  occasional  stirring  for  five  days.  It  was  then  filtered  through 
cloth  to  remove  the  coarse  portions, heated  to  40°  C.  for  two  hours, 
and  finally  filtered  through  folded  filters,  and  preserved  in  bottles. 
To  prepare  the  pancreas  solution  used  in  the  process  of  digestion, 
250  c.c.  of  the  above  described  solution  were  mixed  with  750 
c.c.  of  soda  solution.  The  soda  solution  contained  5  grammes  of 
carbonate  of  soda  dissolved  in  750  c.c.  of  water.  The  pancreas 
solution  thus  prepared  was  heated  for  one  to  two  hours  at  37-40° 
C,  filtered  to  remove  any  flocky  precipitate  and  one  hundred  c.c. 
used  for  each  test. 

The  results  of  the  pepsin-pancreas  digestion  were  as  follows  : 

Per  cent,  of  nitro- 
gen digested. 

I.  Sole  leather  finely  ground 80.98 

II.  Same  leather  after  being  heated  6  hours  at  110°  C.  in 

pressure  bottles  with  water 97-23 

III.  Coarse  leather  (free  from  fat) 52.00 

IV.  Philadelphia  tankage 90.64 

V.  Dried  blood 99-13 


I02  AgRICULTURAI<  SciENCK.  Vol.  VIII.  No.  3. 

The  above  results  are  all  very  high,  but  this  is  not  surprising, 
for  the  action  of  dilute  alkalies  on  leather  is  well  known  and  has 
been  several  times  referred  to.  In  the  present  case,  after  the  var- 
ious leathers  had  been  submitted  to  the  pepsin  digestion,  there 
appeared  to  be  no  very  great  change  either  in  their  appearance 
or  bulk.  Blood  on  the  other  hand  was  nearly  all  dissolved  by 
the  pepsin  solution.  As  soon,  however,  as  the  leathers  were  sub- 
mitted to  the  action  of  the  pancreas  solution  a  decided  change 
was  noted.  The  solution  became  quite  dark  in  color  and  the 
larger  part  of  the  leather  went  into  solution.  While  this  method 
indicated  a  greater  availability  on  the  part  of  the  sole  leather 
after  it  had  been  submitted  to  steam  pressure  it  nevertheless  did  not 
give  a  correct  idea  of  the  digestibility  and  consequent  availability 
of  the  leather  when  compared  with  the  dried  blood. 

The  substances  were  therefore  submitted  to  the  action  of  the 
pepsin  solution  alone  with  results  as  follows  : 

Percentage  digesti- 
bility of  nitrogen. 

I.  Sole  leather, i3-7o 

II.  Sole  leather  after  steam  pressure 34-40 

III.  Coarse  leather 

IV.  Philadelphia  tankage 42.30 

V.  Dried  blood. 97.8o 

These  results  coincide  very  closely  with  those  obtained  by  other 
investigators.  The  sole  leather  itself  proved  very  indigestible. 
It  is  possible  that  it  might  have  proved  somewhat  less  so  if  no 
hydrochloric  acid  had  been  added  during  the  digestion.*  The  sole 
leather  after  being  subjected  to  the  action  of  the  steam  pressure 
had  a  digestibility  of  34.40  per  cent.,  which  coincides  with  re- 
sults obtained  by  others  for  prepared  leather  as  the  following 
samples  show  : 

Percentage  of  nitro- 
gen digested. 

Leather  cooked  and  roasted  (Stutzer) 39«i9 

Roasted  leather  meal  ( Shepard  and  Chazal)  37 .80 

Leather  by  benzine  process  (Johnson) 35-90 

Leather  by  superheated  steam  (Johnson) 33-30 

While  then  the  action  of  steam  and  heat  renders  the  leather 
somewhat  more  digestible  and  probably  more  available  in  the  soil, 
it  still  has  a  digestibility  below  50  per  cent.  Only  the  very  poor- 
est kinds  of  animal  matter  reach  this  low  figure  (50).  The  so 
called  Philadelphia  tankage  was  also  below  50  per  cent,  digestible 

*  Conn.  Exp.  feta.,  1886,  p.  122. 


1894.  Agriculturaiv  Scidnck.  103 

and  may  be  classified  with  the  steamed  or  roasted  leathers  as  re- 
gards its  value.  It  is  to  be  noted,  as  before  mentioned,  that  the 
dried  blood  was  nearly  all  digested  by  the  action  of  the  pepsin 
solution  and  may  be  regarded  as  a  very  excellent  standard  with 
which  to  compare  the  various  leathers. 

General  Conclusions  Relative  to  Raw,  Roasted  or  Steamed 

Leather. 

The  results  of  the  combined  experiments  in  the  field  and  in  pots 
together  with  artificial  digestion  experiments,  and  nitrifica- 
tion experiments,  indicate  that  leather,  either  raw,  roasted  or 
steamed,  is  a  very  slow  acting  form  of  nitrogen  as  a  source  of 
plant  food.  It  certainly  would  be  fraudulent  to  sell  it  in  mixed 
fertilizers  as  a  source  of  organic  nitrogen,  and  the  Masachusetts 
fertilizer  law  distinctly  forbids  it  to  be  thus  utilized.  Carefully 
conducted  experiments  by  Wagner  give  it  a  relative  value 
of  20,  nitrate  of  soda  being  equal  to  100.  From  the  mass  of  evi- 
dence at  our  command  it  would  seem  that  this  figure  about  ex- 
presses its  relative  worth  as  a  direct  source  of  plant  food.  If  it 
is  offered  for  sale  as  a  fertilizer,  it  should  be  sold  as  leather. 
When  nitrogen  in  organic  matter  has  a  value  of  16  to  18  cents 
per  pound,  nitrogen  in  raw,  steamed  or  roasted  leather  should 
be  worth  but  3  to  6  cents  per  pound. 

The  Action  of  Sulfuric  Acid  on  Leather. 

D  eh  era  in  and  others  suggest  that  if  leather  be  dissolved  in 
sulfuric  acid,  its  nitrogen  will  be  made  as  valuable  as  that  in 
any  form  of  animal  matter.  No  experiments,  however,  are 
brought  forward  to  prove  such  a  statement,  but  it  is  generally  un- 
derstood that  many  European  manufacturers  thus  turn  leather 
waste  to  account.  In  order  to  study  this  question  more  closely, 
a  number  of  experiments  were  carried  out  by  the  writer,  a  few  of 
which  are  presented  below. 

Experiment  I. 

Sixty-five  grammes  of  50°  B.  sulfuric  acid  were  heated  in  a 
porcelain  dish  over  a  waterbath  to  about  90°  C.  and  12  grammes 
of  leather  gradually  added.  A  dark,  thick  fluid  resulted.  Thirty 
c.c.  of  water  were  then  added  to  dilute  the  thick  fluid  somewhat. 


I04  AgrICUI.TURAI<  SCII;nCE.  Vol.  VIII.  No.  3. 

and  bone  ash  was  employed  to  dry  off  the  resulting  semi-fluid 
mass.  One  hundred  and  thirty-six  grammes  of  superphosphate 
were  obtained,  which  gave  no  tannic  acid  reaction. 

Experiment  II. 

To  30  grammes  of  50°  B.  sulfuric  acid  heated  as  above  described, 
were  added  12  grammes  of  leather.  A  dark,  thick  paste  was  ob- 
tained, to  which  were  added  25  c.c.  of  water,  and  33  grammes  of 
bone  ash.  Seventy-three  grammes  of  superphosphate  were  ob- 
tained.    The  reaction  of  tannic  acid  was  not  strong. 

Analyses  of  the  two  products  were  made  as  follows  : 

I.  11. 

Per  cent.  Per  cent. 

Moisture 18.03  15-59 

Soluble  phosphoric  acid 14.84  11.80 

Reverted        "            "      .69  1.50 

Insoluble       "            " 1.43  3.38 

Total               "            "      16.96  16.68 

Nitrogen                            0.70  1.20 

Experiments  III,  IV,  V,  VI. 

The  previously  described  Philadelphia  tankage  was  used  in 
these  experiments,  and  South  Carolina  floats  in  place  of  bone  ash. 
The  objects  in  view  were  to  see  (a)  how  much  leather  could  be 
used  without  giving  a  tannic  acid  reaction,  (b)  to  note  if  possible 
to  what  extent  the  leather  interfered  with  the  action  of  the  sul- 
furic acid  upon  the  floats,  (c)  to  notice  the  approximate  percent- 
age of  available  phosphoric  acid  and  nitrogen  resulting,  (d)  to  see 
if  any  nitrogen  in  the  resulting  superphosphates  was  soluble  in 
water,  (e)  to  note  the  amount  of  nitrogen  in  the  superphosphate 
artificially  digestible  by  Stutzer's  solution.  To  make  this  latter 
estimation  (e),  5  grammes  of  superphosphate  were  stirred  with 
water,  filtered,  and  washed  till  the  wash  water  was  no  longer 
acid.  The  portion  not  soluble  in  water  was  treated  with  pepsin 
solution. 

Experim-ent  III. 

To  30  grammes  of  50°  B.  sulfuric  acid  after  heating,  previously 
described,  were  added  12  grams  of  Philadelphia  tankage.  A 
thick,  black  dough  resulted.  It  was  diluted  with  25  c.  c.  of 
water,  appearing  then  as  a  thick  black  fluid.  To  this  fluid  were 
added  60  grammes  of  floats.     The  resulting  superphosphate,  after 


l894-  AgRIC"UI<TURAL  SCIEJNC:^.  IO5 

drying  in  the  air  for  24  hours,  weighed  102  grammes.   The  tannic 
acid  reaction  was  quite  strong. 

Experhnent  IV. 

To  30  grammes  of  50°  B.  acid  were  added  25  c.  c.  of  water  and 
70  grammes  of  floats.  The  dry  superphosphate  weighed  10 1.5 
grammes. 

Experiment  V. 

To  30  grammes  of  50°  B.  acid  were  added  9  grammes  of  Phil- 
adelphia tankage,  which  resulted  in  a  medium  thick  paste. 
Twenty  c.  c.  of  water  and  48.5  grammes  of  floats  were  afterwards 
added.  The  dry  superphosphate  weighed  88  grammes,  and  gave 
no  tannic  acid  reaction. 

Experiment   VI. 

To  30  grammes  of  40°  B,  acid  9  grammes  of  Philadelphia  tankage 
were  added,  resulting  in  a  medium  thick  paste.  This  paste  was 
diluted  with  20  c,  c.  of  water,  and  50  grammes  of  floats  were  put 
in.  Seventy-nine  grammes  of  superphosphate  were  obtained, 
which  gave  a  strong  tannic  acid  reaction. 

These  several  products  were  analyzed. 

III.  IV.  V.  VI. 

Per  cent.  Per  cent.  Per  cent.  Per  cent. 

Moisture 14.14  I4-I3  14.86            

Soluble  phosphoric  acid 6.78  7.30  7.80            

Reverted        "              "   1.22  1.60  0.44            

Insoluble       "              "  5.50  6.66  4.94            

Total               "              "  13.50  15.56  13.18            

Total  nitrogen 0.81           0.87  1.03 

Nitrogen  after  artificial  digestion 0.37           0.25  0.41 

Per  cent,  of  total  nitrogen  digested 54                71  60 

Soluble  nitrogen trace            trace            

It  would  appear  that  9  grammes  of  leather  were  all  that  could 
be  added  to  30  grammes  of  sulfuric-acid  without  getting  the 
tannic-acid  reaction.  When,  as  in  Experiment  III.,  12  grammes 
of  leather  were  added,  the  reaction  for  tannic  acid  was  quite 
marked,  and  the  nitrogen  in  the  superphosphate  had  a  digestibil- 
ity of  but  54  per  cent.  Experiment  VI.  indicates  that  40°  B. 
sulfuric  acid  was  not  quite  strong  enough  to  thoroughly  disinte- 
grate the  9  grammes  of  leather,  for  the  tannic  acid  in  the  super- 
phosphate was  easily  recognized,  and  the  nitrogen  was  but  60 
per  cent,  digestible.    When  9  grammes  of  the  Philadelphia  tank- 


io6  Agricui.turai<  Science.         Vol.  viii.  No.  3. 

age  were  dissolved  in  30  grammes  of  50°  B.  acid,  no  tannic  acid 
could  be  recognized,  and  70  per  cent,  of  the  total  nitrogen  was 
digestible.  This  is  probably  the  average  percentage  of  organic 
nitrogen  that  would  be  found  digestible  in  mixed  fertilizer,  as 
offered  for  sale  in  our  markets.  Such  a  result  is  quite  encourag- 
ing. It  would  seem  from  the  analysis  of  IV.  that  the  leather  had 
not  seriously  interfered  with  the  action  of  the  sulfuric  acid  upon 
the  floats.  We  have  in  the  four  experiments  above  cited,  added 
rather  too  much  phosphate  rock  and  water,  and  in  the  two  follow- 
ing experiments,  less  were  added. 

Experiment  VII. 

To  30  grammes  of  50°  B.  acid  9  grammes  of  Philadelphia  tank- 
age were  added,  and  then  12  c.c.  of  water.  To  the  thick  fluid 
resulting,  41  grammes  of  floats  were  added.  After  standing  24 
hours,  the  material  could  be  easily  handled,  and  weighed  71.5 
grammes. 

Experiment  VIII. 

To  30  grammes  of  50°  B.  acid  9  grammes  of  Philadelphia  tank- 
age were  added,  producing  a  thick  pasty  mass.  Without  the 
addition  of  water,  28  grammes  of  floats  were  stirred  in,  and  after 
24  hours,  the  mass  weighed  63  grammes.  The  phosphate  was 
quite  black  in  color,  and  sticky.  It  needed  at  least  5  to  7  grammes 
more  floats,  before  it  could  be  easily  handled.  It  was  plain  that 
the  sulfuric  acid  was  not  all  neutralized.  If  no  water  were  added 
to  dilute  the  thick  pasty  mass,  it  would  be  very  difficult  to  work 
in  the  floats  should  large  quantities  be  mixed. 

ANAI^YSES. 

VII.  vin. 

Per  cent.  Per  cent. 

Moisture 17-95  16.95 

Soluble  phosphoric  acid 6.79  5.99 

Reverted        "  "    2.16  1.62 

Insoluble        "  "    1-94  1-56 

Total  "  "   10.89  9-17 

Total  nitrogen 0.90  1,06 

In  Experiment  VII.,  8.95  per  cent,  of  available  phosphoric  acid 
was  obtained,  with  but  1.94  per  cent,  of  insoluble  acid,  and  0.90  per 
cent,  of  nitrogen  ;  the  phosphate  was  also  in  good  mechanical 
condition  and  gave  no  tannic  acid  reaction.  The  proportions  of 
water,  sulfuric  acid,  floats,  and  leather,  appear  to  be  about  correct, 


1894.  Agricultural  SeiENCE.  .         107 

and  the  percentages  of  available  phosphoric  acid  and  nitrogen  as 
high  as  could  be  expected,  with  floats  as  a  dryer. 

Experiment  IX. 

In  Experiments  III  to  VIII  Philadelphia  tankage  was  used  as 
a  source  of  leather. 

In  this  experiment,  pure,  fine  ground  sole  leather  was  used, 
to  see  if  the  sulfuric  acid  acted  as  strongly  upon  the  pure 
leather,  as  upon  the  prepared  article.  To  30  grammes  of  50  B. 
acid  were  added  9  grammes  of  sole  leather,  20  c.c.  of  water,  and 
60  grammes  of  floats. 

The  resulting  phosphate  weighed  98.5  grammes 

Analysis  gave  the  following  results  : 

Per  cent. 

Total  nitrogen  in  the  superphosphate 0.71 

"  "         after  digestion 0.22 

"  "         digested  per  cent 69. 

Nitrogen  soluble  in  water 0.047 

Percent,  of  soluble  nitrogen 6.62 

No  tannic  acid  could  be  detected  in  this  superphosphate.  The 
digestion  test  was  made  in  triplicate,  and  showed  that  the  pure 
sole  leather,  after  treatment  with  sulfuric  acid,  was  quite  as  di- 
gestible as  the  steamed  or  roasted  leather  after  a  similar  treat- 
ment, and  as  digestible  as  the  average  animal  matter  sold  for 
fertilizing  purposes. 

In  order  to  still  further  study  the  value  of  dissolved  leather  as 
a  source  of  plant  food,  pot  experiments  are  now  in  progress  at 
the  station,  and  the  results  will  be  reported  later. 

Practical  Deductions. 

The  various  experiments  made  would  indicate  that  leather,  sul- 
furic-acid,  water  and  floats  should  be  mixed  in  about  the  fol- 
lowing relative  proportions  : 

2,000  lbs.  50°  B.  sulfuric  acid 

600  "     ground  leather 

800  "     water 
2,700  "     floats 

The  resulting  mixture,  when  in  fairly  dry  condition,  would 
weigh  approximately  5,000  lbs.,  shrinking  about  18  to  20  per 
cent.     It  would  have  approximately  the  following  composition  : 


io8  Agricultural  Science.  Vol.  viii.  No.  3. 

Per  cent. 

Moisture 18.00 

Available  phosphoric  acid 8.50 

Insoluble  "  "     2.00 

Total  "  "     10.50 

"    nitrogen 0.90 

Two  thousand  pounds  of  sulfuric  acid  will  not  take  up  more  than 
600  lbs.  of  leather  and  render  the  leather  70  per  cent,  digestible. 
If  more  is  added,  part  of  the  latter,  whether  roasted  or  raw,  will 
not  be  thoroughly  acted  upon  by  the  acid.  With  600  lbs.  of 
leather,  a  thick  paste  results  which  must  be  diluted  somewhat 
with  water  in  order  to  allow  the  sulfuric  acid  to  act  freely  upon 
the  floats.  If  bone  ash  should  be  used  as  a  dryer  in  place  of 
ground  phosphate  rock  a  higher  percentage  of  available  phos- 
phoric acid  and  of  nitrogen  would  result,  as  Experiments  I  and  II 
indicate. 

Before  submitting  the  leather  to  the  action  of  the  sulfuric-acid, 
it  would  undoubtedly  be  better,  after  extracting  the  fat,  to  steam 
or  roast  it,  in  order  that  it  may  be  easily  pulverized.  Raw.  un- 
treated leather  is  ground  only  with  difi&culty,  and  if  the  mechani- 
cal condition  of  the  leather  were  poor,  the  action  of  the  sulfuric 
acid  would  be  imperfect 

Resume— Action  of  Sulfuric  Acid  Upon  Leather. 

Artificial  digestion  experiments  show  that  the  nitrogen  in  either 
untreated,  steamed  or  roasted  leather  after  being  acted  upon  by 
sulfuric  acid  has  a  digestibility  of  70  per  cent.  If  pot  and  field 
experiments  corroborate  the  digestion  experiments,  it  would 
make  plain  that  the  nitrogen  in  leather  after  being  thus  treated 
would  be  as  available  as  a  Source  of  plant  food  as  the  nitrogen  in 
the  average  fish,  blood,  etc. 

Whether  it  would  be  practicable  from  an  economical  standpoint 
to  thus  utilize  the  leather  waste  is  of  course  another  question 
which  must  be  answered  by  practical  experiments, 

Mass.  State  Experiment  Station, 
April,  1894. 


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Mt 


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